The purpose of the proposed research is to study the relationship among the RNA's of avian RNA tumor viruses and between these and endogenous virus nucleic acids in uninfected host cells. Previous studies, in this laboratory and others, have shown that exogenous and endogenous avian tumor viruses are closely related to each other, and differ both by base substitutions in some regions and the acquisition of non-viral host sequences in other regions. The project will divide itself into two parts: First, to study in great detail the structure of tumor virus genomes and second, to use the information gained to analyze the nucleotide sequence relationships between these tumor-producing viruses and both fully expressed and partially expressed endogenous viral genes. Particular attention will be paid to regions of the genome coding for cell transformation and to non-coding regions involved in DNA synthesis and mRNA processing. For these purposes we will use very sensitive methods consisting of combinations of nucleic acid hybridization and RNA fingerprinting. It is expected that the results of this project will allow us to infer, at a molecular level, the mechanisms and events which relate tumor-producing viruses and benign cell information.